Nikolaos Athanasopoulos

Unconstrained and constrained stabilisation of bilinear discrete-time systems using polyhedral Lyapunov functions

The constrained and unconstrained stabilisation problem of discrete-time bilinear systems is investigated. Using polyhedral Lyapunov functions, conditions for a polyhedral set to be both positively invariant and domain of attraction for systems with second-order polynomial nonlinearities are first established. Then, systematic methods for the determination of stabilising linear feedback for both constrained and unconstrained bilinear systems are presented. Attention is drawn to the case where no linear control law rendering the pre-specified desired domain of attraction positively invariant exists. For this case, an approach guaranteeing the existence of a possibly suboptimal solution is established.

Invariant set computation for constrained uncertain discrete-time linear systems

In this article a novel approach to the determination of polytopic invariant sets for constrained discrete-time linear uncertain systems is presented. First, the problem of stabilizing a prespecified initial condition set in the presence of input and state constraints is addressed. Second, the problem of computing an estimate of the maximal positively invariant or controlled invariant set for this class of systems is investigated. An illustrative example, showing the effectiveness of the proposed methods, is presented.

Constrained Stabilization of Bilinear Discrete-Time Systems Using Polyhedral Lyapunov Functions

In this paper, the stabilization problem of discrete-time bilinear systems by linear state-feedback control is investigated. First, conditions guaranteeing the positive invariance of polyhedral sets with respect to nonlinear systems with second order polynomial nonlinearity are established. Then these results are used for the determination of linear state-feedback unconstrained and constrained control laws making a prespecified polyhedral set a domain of attraction of the resulting closed-loop system.

New generation biofuel: continuous acidogenesis of sucrose-raffinose mixture simulating vinasse is promoted by γ-alumina pellets

BackgroundThis investigation comprises a contribution on the production of a new generation biofuel using the industrial liquid waste of bioethanol distilleries, known as vinasse. This study focuses on the exploitation of vinasse as an acidogenesis substrate for volatile fatty acids and simultaneous ethanol production. These products can be used for ester production, which is the new generation biofuel. Therefore, the aims of the present study are (i) to examine any promotional effect of γ-alumina on acidogenesis of a sucrose-raffinose mixture simulating vinasse, (ii) to study the operational stability of the continuous acidogenesis of sucrose and raffinose and subsequently of vinasse, and (iii) to determine the volatile fatty acid chemical composition and ethanol formation.ResultsBatch acidogenesis of sucrose and raffinose mixtures showed that γ-alumina promoted fermentation leading to an increase in the volatile fatty acid yield factor from 40% to 95% compared to free cells. The application of the system in continuous mode for more than 3xa0months showed that the continuous volatile fatty acid productivity obtained was higher than 7xa0g/L/day. Lactic acid was the predominant acid when sucrose and raffinose were used while butyric acid in the case of vinasse. The highest volatile fatty acid concentration reached was 19xa0g/L for vinasse.ConclusionsA promoting effect of γ-alumina in acidogenic fermentation of sucrose-raffinose and vinasse is reported. Continuous acidogenesis of sucrose-raffinose mixtures and vinasse using γ-alumina with immobilized cells showed high operational stability (more than 3xa0months). These findings result in easy scale up of the process that will produce a high annual added value of

Use of earthworm biotechnology for the management of anaerobically stabilized effluents of dried vine fruit industry

11,000,000 in a daily bioethanol production plant of 50,000xa0L.

Continuous acidogenesis of sucrose, raffinose and vinasse using mineral kissiris as promoter.

SummaryAnaerobically stabilized effluents of dried vine fruit industry were successfully treated in earthworm filters. The species L. rubelus was used. At COD loadings of up to 0.2 Kg COD/m2d the reactors responded well for an operation period of 15 months when experiments ceased. COD removal was 95% for loadings of 0.10 and 0.15 Kg COD/m2d. Earthworm biomass seems to be in its upper bearing capacity of approximately 2 Kg/m2 and did not increase seriously with time. Temperature change did not have any counter effect on the process.

Cotton yarn and fabric finishing wastewater treatment using an anaerobic expanded bed reactor.

The use of kissiris as promoter (culture immobilization carrier) in anaerobic acidogenesis of sucrose, raffinose and vinasse is reported. Initially, the effect of pH (4-8) and fermentation temperature (18-52 °C) on the accumulation of low molecular weight organic acids (OAs) during sucrose acidogenesis, was evaluated. The promoting effect of kissiris was confirmed compared to free cells, resulting in 80% increased OAs production. The optimum conditions (pH 8; 37 °C) were used during acidogenesis of sucrose/raffinose mixtures. A continuous system was also operated for more than 2 months. When sucrose and sucrose/raffinose mixtures were used, lactic acid type fermentation prevailed, while when vinasse was used, butyric acid type fermentation occurred. Total OAs concentrations were more than 14 g/L and ethanol concentrations were 0.5-1 mL/L. Culture adaptation in vinasse was necessary to avoid poor results. The proposed process is promising for new generation ester-based biofuel production from industrial wastes.

Feedback stabilization of Networked Control Systems

Abstract Wastewater from cotton yarn and fabric finishing was treated in an anaerobic expanded bed reactor at 35°C up to a COD loading of 0·63 kg/m3 day. The COD removal varied from 50 to 87% and the production of biogas was 0·06-0·35 litre/g COD removed or 0·015-0·040 vol./vol./day, having 70–80% CH4. At higher COD loading biogas production stopped although COD removal remained approximately at 35%.

A Dual Comparison Principle for the Analysis and Design of Discrete-Time Dynamical Systems

In this paper the stability analysis and control synthesis problems for Networked Control Systems (NCS) with bounded transmission delays (constant and unknown or time-varying) are investigated. First, stability conditions for NCS described by ARMA models are established and a method for the determination of admissible delay range is developed. Then, a linear programming method for the design of linear state-feedback controllers guaranteeing the stability of the system for any delay belonging to a prespecified range is developed. Contrary to the usual approaches based on the use of quadratic Lyapunov functions, a polyhedral Lyapunov approach is adopted for both analysis and synthesis. A control synthesis numerical example is given to illustrate the reduction of conservatism of the tolerable delay range when compared to former results.

Smart patterned surfaces with programmable thermal emissivity and their design through combinatorial strategies

Abstract In this article, two new comparison principles for studying positive invariance and stability of linear and nonlinear discrete-time systems are presented. First, a general comparison principle enabling one to determine necessary and sufficient conditions of positive invariance of sets described by their “border surfaces” is developed. Then, a dual comparison principle describing the dynamics of the “vertices” of these sets is established. Both results can be used for the stability analysis and the control design of nonlinear systems.